The present invention is directed toward a safety apparatus and more particularly toward a safety apparatus in the form of a descent controller used by a workman or other person to control his descent down a rope. The descent controller of the present invention also includes a centrifugal brake that prevents the rapid descent of the workman.
Descent control devices have been developed, all with the objective of lowering a person or load from a higher to a lower elevation. These devices have taken many forms and have utilized a variety of elements capable of providing a mechanical advantage together with a braking mechanism. Safety features, such as deadman and panic control features, are equally important, particularly when the device is used for descent, escape, or rescue purposes.
In more recent years, concerns with occupational safety have led to the development of mechanisms which enable a worker to lower himself from an elevated position such as a scaffold, crane, lift truck or platform in the event of an emergency. The equipment is, in many respects, similar to known fire escape devices, mountain climbing equipment, and military equipment.
A descent load lowering device in the form of a small cylindrical drum about which a rope is wound to provide a descent braking function is disclosed in U.S. Pat. No. 4,550,801 to Forrest. The device shown therein includes end plates on each end of a cylindrical drum with apertures on each end plate through which a rope is threaded and wound in two of more turns around the drum. The lower end plate is provided with one or more arcuate tapered slots opening into the rope receiving aperture for engaging and binding the rope in order to increase friction and form somewhat of a brake. The operator grasps and moves the free untensioned end of the rope along a tapered slot to vary the rate of descent or stop it altogether by tensioning and holding the rope in the narrow end of the arcuate tapered slot.
While devices such as shown in the Forest patent have provided some benefit, they take some skill and experience to operate properly. Furthermore, should the workman make a mistake or be injured, there are no safety provisions for automatically controlling his descent or for preventing freefall.
A descent control device with a brake, in the form of a vertical cylindrical drum or capstan about which a rope is wound and a tapered slot through the drum for receiving and releasably gripping the rope along which descent is made, together with a releasable locking end plate, is described in U.S. Pat. No. 4,883,146 to Varner et al. As with Forrest, the device shown in the Varner et al. patent includes end plates on each end of a vertical cylindrical drum or capstan with apertures on each end plate through which a rope is threaded. The rope is wound in two or more turns around the drum. The lower plate is provided with an arcuate tapered slot opening into the rope receiving aperture for engaging and binding the rope in order to provide a brake.
Unlike Forrest, however, the rope of Varner et al. is mechanically forced into the aperture by a locking end plate rotatably mounted on the capstan below the lower end plate. The locking plate includes an aperture for loosely receiving the rope. A spring rotatably biases the locking plate to releasably and forcibly urge the rope into the narrowed tapered slot in the lower end plate for locking the rope against movement on the capstan. By rotating the locking plate against the force of the spring the rope can be progressively released from the tapered slot.
Apparently recognizing the difficulty in operating the device of the Varner et al. '146 patent, the inventors designed improvements thereon and obtained U.S. Pat. Nos. 5,038,888 and 5,131,491. These improvement patents, however, continue to rely on the original concept of forcing a rope into an arcuate slot to control decent. These improved patented devices can still be difficult to operate because of the manner in which they must be manipulated to control ones descent.
In addition, and perhaps more importantly, none of the Forrest or Varner et al. devices includes a mechanism such as an additional safety brake or the like. Such a brake could prevent serious injury to a workman in the event of an unwanted rapid descent or freefall due to a malfunction of the descent controller or due to the workman improperly using the device from panic or as a result of an injury. While positive safety brakes are known, none has ever been combined with a descent controller.